As contact detecting apparatuses based on the conventional technology, there have been the ones which detect a contact between a machining tool and a work according to a voltage change in a servo motor for driving a main axis as disclosed in Japanese Patent Laid-Open Publication No. SHO 60-22113, or the ones which determine that a slide table has contacts a stopper located at a fixed position or a stroke restricting section (reference position setting member) by checking that a current flowing in a motor for driving the slide table has becomes an excessive current as disclosed in Japanese Patent Laid-open Publication No. SHO 58-124907.
In the conventional type of contact detecting apparatuses, to improve reliability of contact detection, it is necessary to continue driving a movable body such as a tool or a slide table even after the movable body actually contacts an object for contact such as a work or a reference position setting member for a certain period of time in the same direction for the purpose to obtain a relatively large and clear load fluctuation component, which may result in damages of the movable body and object for contact.
Especially, when the movable body is a sharp tool such as a bite, as a biting area on a work is small, load fluctuation is fine, and sometimes an accurate contact position can not be detected. To make the load fluctuation component larger, it is required to make the biting rate large or to increase the thrust-in speed, and as a result a large biting damages are generated in the work and also damages such as chipping are given to a tool such as a bite.